Thermochemical lancing and cutting powders and method of preparing same for use in oxygen suspension



United States Patent THERMOCHEMICAL LANCING AND CUTTING POWDERS ANDNEETHOD 0F PREPARING SAME FOR USE IN OXYGEN SUSPENSION Horace Freeman,Cap de la Madeleine, Quebec, Canada, a'ssignor to Freeman Corporation,Cap de la Madeleine, Quebec, Canada No Drawing. Application March 31,1958 Serial No. 724,929

7 Claims. (Cl. 75-.5)

This invention relates to a new and improved mixture of metal powdersfor use in cutting high heat, refractory materials, such as, chrome andnickel alloys, cast iron, and all manner of non-metallic, refractorymaterials, such as, fire brick, magnesite brick, aluminum, chrome, slag,concrete rock, and to a method of preparing the same in a form welladapted to be suspended in an oxygen reacting stream during itspassagethrough a cutting torch or lance.

It has long been known that steel, when raised to the ignitiontemperature, can rapidly be cut with a stream of oxygen. Theconventional cutting torch, therefore, consists of an oxy-fuel gasflame, to raise the temperature of the steel to the ignition point and asecondary means of directing a stream of oxygen on to the preheatedsteel to accomplish the cutting action. Such a procedure however, isineffective for the cutting of the refractory materials aboveenumerated.

In torch cutting or lancing refractory materials it is well-known todirect streams of iron powder and oxygen into the reaction zone topermit a continuous cutting action, due to the thermochemical fiuxingreaction so produced. Because of its relatively low ignitiontemperature, the iron powder is normally conveyed to the cutting torchor lance by a relatively inert gas stream. This gas acts as a diluentfor the products of combustion and carries heat away from the reactionzone. duces the efiective temperature in the reaction zone, whereas,higher temperatures are desired to increase the rate of cutting orfluxing or for other purposes.

The heat value of iron oxidized to ferric oxide is only slightly over3,000 B.t.u. per pound, but when iron powder is oxidized or burned inpure oxygen, the temperature produced is well above the melting pointsof alloy steels, due to the fact that the oxygen isabsorbed into themolten iron oxide and no heat is carried away from the torch flame byinert gas. The molten iron oxide fluxes and thereby cuts into refractorymetals and materials such as cast iron, alloy steel, firebrick, slag,concrete, etc.

' Attempts have been made to convey iron powder to the torch or lancewith oxygen to avoid the use of air or inert gas, in order further toincrease the temperature and rate of cutting, but these have not provensuccessful, due to undue heating of the torch or lance and consequentflashbacks in the torch or lance. Serious explosions have resulted fromconveying iron powder and mixtures of iron powder and aluminum powder inoxygen. It will be recognized that a lance is a metal pipe or tube usedto convey the powder and oxygen. It may be as long as 20 feet. Its freeend gets quite hot and heat is transmitted backwards into the pipe.

Commercially available iron powders will ignite in oxygen at lowtemperatures, such as a low red heat, and some types ignitespontaneously when exposed to oxygen or even to air at ordinarytemperatures. Commercial iron powder containing less than 0.2% each ofcarbon and silicon, which has been sinteredin a reducing atmosphere ofabout 1,800 F. passing through a standard This re-' "Ere Tyler screen of325 mesh will ignite in oxygen at 700 F. whereas particles of the samepowder larger than 100 mesh ignite only at 860 F. in oxygen and mixturesof these sizes ignite at the lower temperature of 700 F. A powder havingan ignition point of 700 F. has been found too unsafe for use in anoxygen stream. I have found that any inert, powdered, non-metallicmaterial, such as powdered magnesia, added to iron powder will raise itsignition point by simple dilution, but such material is objectionablesince it lowers the ultimate temperature developed by the combustion ofthe iron.

The object of the present invention is to provide a metallic powderwhich has the thermochemical properties which permit its successful andsafe use in a cutting torch or lance with oxygen. More specifically, theinvention contemplates a metal powder composition for the purposedescribed, which has a safe ignition temperature, which may be safelyconveyed with oxygen through the torch or lance, and which at the sametime will develop the desired high temperature and thermochemicalfiuxing action.

The invention also contemplates a method of making such powder in theform of a mixture of metallic particles, which insures provision of thethermochemical properties described.

The metallic cutting and lancing powder of the invention consistsessentially of a mixture of finely divided iron powder, having arelatively low ignition temperature in oxygen, with a finely dividediron alloy powder, refractory toward oxygen while in the solid state butreacting rapidly with oxygen when molten, in such proportions that themixture may be safely conveyed in oxygen through a torch or lance forignition at the surface to be cutaway. That is to say, the mixture iscomposed of iron powder which ignites in oxygen at temperatures of about700 F. and a powder of an alloy of iron, having a higher heat ofoxidation than iron, which ignitesin oxygen at a temperature of not lessthan 1700? F. in such proportions that the mixture will ignite in oxygenonly at a temperature in excess of 700 F., and below 1200" F., that isto say, between a low red heat and a bright red heat.-

According to the invention, the ferrous alloy powder of the mixturecomprises ferro-aluminum, to provide in the mixture 10% or morealuminum. In this connection, it is to be observed the heats ofoxidation of the two metals ofwhich the mixture is composed are: Fe toFe O 3,175 B.t.u. per pound, Al to A1 0 13,218 B.t.u. per pound. V

The mixture should not contain substantially less than 33 /s% norsubstantially more than of free iron powder and the balance the alloypowder, therproportions varying according to the specific use, and thusthe range of temperatures and degree of fluxing action desired. Suchmixtures will not ignite in an oxygen stream in passing through thelance or torch, but will develop higher temperatures than iron aloneupon combustion. At the lower free iron content, the mixture will igniteat a temperature about 1050" F., and at the higher free iron content atapproximately 800 F. The maximum permissible-alloy content is preferredfor reasons of safety. 7 v

It has been found that the ferrous alloy powder used alone in oxygencannot be ignited at the start of the cutting operation without anexcessively hot ignition source on the surface to be cut and, even whenignited, it doesv not burn as fast as the iron powder alone, or as fastas the mixture of the free iron powder and the ferrous alloy.

der during .its passage through the lance and does not bumuntil molten.Thereby, it functions to prevent .igni tion of the powder in passagethrough the torch or lance. The alloy powder of the mixture preferablycontains about. equal proportions Zof iron and aluminum. The alloys ;maybereadily made in an electric furnace. These proportions are preferred,because they provide the most brittle alloy, which is readily convertedto powder, and they provide the mixture with a large proportion of thehigh heat value of aluminum. Moreover, the density of the .alloy is soclose to that of the iron powder that segre gation of thelconstituentsof the mixture does not readily occur. in producing the mixture theironand .the ferro-alloy are each produced in the form of fine powderspreferably passing :60 mesh, with a proportion up to 30% passing 325mesh, with intermediate distribution of sizes. These powders care thenmixed or blended together to form a composition containing notsubstantially less than one- :third, nor substantially more thanfour-fifths of the free iron powder. The preferred mixture for generaluse contains substantially one-third free iron, one-third combined :ironand one-third aluminum, but these proportions may vary widely, accordingto specific use and material being fluxed. The powder should preferablypass through 60 mesh Tyler'screen, and may be finer than this; for exam--ple, it may all pass through a 100 mesh screen, but a minimum ofparticles passing through 325 mesh is preferred, as the finer fractionsdo not flow easily and have -a tendency in the iron fractions topro-ignite. Mixtures 100% passing 100 mesh with 30% passing 325 mesh aresuccessfully used.

Thus when here and elsewhere in this specification and claims, "I usethe term finely divided it is to be understood as being in the range offrom 100% through 60 mesh and up to 30% through 325 mesh.

It is found that, when such mixtures are burned in an adequate supply ofoxygen, the iron content ignites first at the heated surface above avisible red heat of brick, slag, metal or other refractory which is tobe cut, forming immediately iron oxide in highly fluid condition withwhich-the alloy content reacts rapidly in the molten state, formingextremely ;hot and fluid mixtures of iron oxide, aluminum oxide, whichrapidly melt and flux away the surface upon which the flame is impinged.

It will be seen, therefore, ,that while it has previously been proposedto utilize mixtures of iron powder and aluminum or other metal powders,said mixtures must be handled inair or an inert gas stream, which is,inconvenient and reduces the temperature. The .essence of thisinvention"lies in providing a mixture of free iron and refractory iron alloypowders in which the ignition temperature in oxygen is raised by simpledilution to a point at which the powder safely may be carried in oxygenattemperature up to a -low.red heat but which, when ignited at highertemperature, will react rapidly with oxygento develop molten oxidemixtures having higher temperature and having fiuxing propertiessuperiorto those obtained with iron alone. By these means, by raising the heatvalue of the metal powderand making it possible to convey it safely inoxygen, it has-been found possible to cut refractory materials with easeand rapidity.

Another advantage of the composition of this invention, as compared withsimple mechanical mixturesof -iron powder and aluminum powder, or .othermetal powders, lies in the tendency of the elemental powders, .by virtueof their differences in specific gravity, to separate in handling andtransportation, Whereas, the zPDWflcrs ;of this invention are of closerspecific gravity and, :therefore, not subject to gravity separation,such as :by vibration during transportation. It is obvious that, foruniform continuity of safe operation, such separation must be a oi ed.

I am aware that, in the past, some users have mixed elemental ironpowderand elemental aluminum powder immediately prior to use for,cutting and lancing. Such procedure is attended by hazard in the mixingoperation and, more particularly, by hazard in the use of such amechanical mixture, due @to the well-known tendencies of these finelydivided metals to pre-ignite, which hazards are overcome by thisinvention.

Mechanical mixtures of some elemental metal powders, such as iron andaluminum or magnesium, are subject to spontaneous combustion .and todeterioration .by slow oxidation by air, ,oxygen, moisture, or othergases, which render them hazardous in preparation, storage and .use, andslow deterioration detracts fromiheir ultimate usefulness. Thecompositions of this invention are not sub ject to such spontaneouscombustion or deterioration.

The invention has been-described with reference to preferred embodimentsin which specific alloys, quantities and proportions are given. It is to'be understood that these specific alloys, quantities and proportionsare merely exemplary of the invention and should not be construedaslimitations. Such embodiments of the invention :as come within thescope and purview of the appended claims are to be considered as partofthis disclosure.

What is claimed is:

1. A thermochemical metalmixture for safetorch cutting and lancing withoxygen, consisting essentially of a mixture of iron powder having arelatively low ignition temperature and a binary alloy powder consistingessentiallyof substantially equal parts of iron and aluminum having arelatively high ignition temperature, the mixture containing not morethan parts of said iron powder and the balance being powder derived fromsaid binary alloy, whereby theignition temperatureof the mixture iscontrolled to prevent ignition of the mixture in transit with oxygentothe discharge end of the torch or lance. 2 A mixture as claimed in claim.1 wherein the iron powder has an ignition point in oxygen about 700 F.and said alloy powder has an ignition point in oxygen of at least l700F.

3. A mixture as claimed in claim 1 wherein the iron powder has anignitionpoint in oxygen about 700 F. and said alloy powder has anignition point in oxygen of at least 1700 F. and wherein said ironpowder and saidiron alloying powder are combined in such proportionsthat the ignition point ofthe mixture in oxygen is between about 800 F.and about 1050" F.

p 4. A mixture as claimed in clairnl, in 'which the free iron contentforms at least one-third of the mixture and the balance being alloypowder, said alloy powder being refractory to oxygen while in the solidstate, but capable of rapid oxidation while in the molten state, therebygenerating higher temperature than the oxidation of iron powder alone. i

5. A mixture as ,claimed in claim 1 and wherein said mixturecomprisesbetween 33 /a% and by weight of iron powder and the remainderiron-aluminum alloy powder, said alloy being such as to provide at least10% by weight of aluminum in the total mixture.

.6. A process of producing ferrous metalpowders for torch cutting withoxygen which comprises mixing finely divided iron, having a low ignitiontemperature in oxygen, with finely dividedbinary alloy consistingessentially of substantially equal parts of iron .and aluminum, saidalloy having a high ignition temperature in oxygen, the iron powderconstituting at least.30% ofthe mixture and the balance being powderderived from said binaryalloy, whereby the ignition temperature .ofthefmixture is raised substantially above that to which the mixture issubjected in passing insuspension in oxygento the nozzle ,of the torchor lance. a 7. A process of producing a thermochemical powder :for torchcutting with oxygen which comprises crushing to powder formterm-aluminum having substantially equal proportions of iron andaluminum and having an ignition References Cited in the file of thispatent point in oxygen of at least 1700" F., and mixing with the alloypowder finely divided iron to reduce the ignition FOREIGN PATENTS pointof the mixture to not substantially less than 800 6, 0 Gr at Britain g-16, 1948 F. and thus provide a safe torch or lance cutting mixture 5696,840 Great Britain Sept. 9, 1953 having an enhanced heat value andfluxing action.

1. A THERMOCHEMICAL METAL MIXTURE FOR SAFE TORCH CUTTING AND LANCINGWITH OXYGEN, CONSISTING ESSENTIALLY OF A MIXTURE OF IRON POWDER HAVING ARELATIVELY LOW IGNITION TEMPERATURE AND A BINARY ALLOY POWDER CONSISTINGESSENTIALLY OF SUBSTANTIALLY EQUAL PARTS OF IRON AND ALUMINUM HAVING ARELATIVELY HIGH IGNITION TEMPERATURE, THE MIXTURE CONTAINING NOT MORETHAN 75 PARTS OF SAID IRON POWDER AND THE BALANCE BEING POWDER DERIVEDFROM SAID BINARY ALLOY, WHEREBY THE IGNITION TEMPERATURE OF THE MIXTUREIS CONTROLLED TO PREVENT IGNITION OF THE MIXTURE IN TRANSIT WITH OXYGENTO THE DISCHARGE END OF THE TORCH OR LANCE.